Add Vite setup documentation and working example

Convert app/example-ui components to use .jsx extensions as expected by Vite.

Close #433
Fix #265

Author: Dovakeidy

README.md

@@ -16,6 +16,7 @@ Development monorepo for "React Strict DOM".
   * [example-ui](https://github.com/facebook/react-strict-dom/blob/main/apps/example-ui)
   * [expo-app](https://github.com/facebook/react-strict-dom/tree/main/apps/expo-app)
   * [nextjs-app](https://github.com/facebook/react-strict-dom/blob/main/apps/nextjs-app)
+  * [vite-app](https://github.com/facebook/react-strict-dom/blob/main/apps/vite-app)
   * [platform-tests](https://github.com/facebook/react-strict-dom/blob/main/apps/platform-tests)
 * `packages`
   * Contains the individual packages managed in the monorepo.